Peter Horrocks, head of global news at the BBC, called on the Iranian government to 'repudiate the actions of its officials'. Photograph: Martin Godwin for the Guardian

Iran has arrested, questioned and intimidated relatives of journalists working for the London-based BBC Persian Television in its latest crackdown on press freedom.

It comes just two weeks after the arrests in Tehran of documentary film-makers accused of secretly working inside the country for the Farsi-language service.

Peter Horrocks, the head of global news at the BBC, said on Wednesday that relatives and friends of around 10 of the channel's Iranian staff who work in the UK have been approached by the authorities. He called on the Iranian government to "repudiate the actions of its officials" and urged the British government to "deter the Iranian government" from attempts to undermine free media.

"Passports have been confiscated, homes searched and threats made. The relatives have been told to tell the BBC staff to stop appearing on air, to return to Iran, or to secretly provide information on the BBC to the Iranian authorities," he wrote on the BBC blog The Editors.

"Many of our Iranian employees who live in London are fearful to return to their country because of the regime's attacks on the BBC. But although those journalists are beyond the direct reach of their government they are now subject to a new underhand tactic," he added.

Horrocks also highlighted the plight of the imprisoned film-makers who Iran said have "painted a black picture of Iran and Iranians" by supplying the BBC with reports misrepresenting the country. They have been identified as four documentary film-makers – Hadi Afarideh, Naser Saffarian, Mohsen Shahrnazdar and Mojtaba Mirtahmasb – and a producer and distributor, Katayoun Shahabi.

The BBC says they are independent and have no links with the television channel. It has previously shown films belonging to some of them after buying rights but it insists they have never been commissioned by the channel.

Since the arrests, several Iranian officials have stepped forward to condemn the film-makers as "a group of terrorists, Baha'is, communists" and, in the words of Iran's minister of intelligence, Heydar Moslehi, "devil-worshippers".

BBC Persian, which has also been accused by the Iranian regime of collecting information on behalf of MI6, is blocked in the country but millions of Iranians watch satellite channels illegally.

Observers have seen the recent developments as Iran's response to the broadcast of a documentary made by BBC Persian on the Iranian supreme leader, Ayatollah Ali Khamenei, called The Ways of the Ayatollah. The programme – produced by Iranian journalist Bozorgmehr Sharafedin and shown in mid-September – was the first of its kind to touch the taboo issue of Khamenei's leadership.

Iranian documentary film-maker Maziar Bahari, who was arrested in June 2009 and kept in jail for 118 days, said dozens of other people in Iran have also been summoned to Iran's security departments in recent weeks after the broadcast of the documentary.

"They basically want to cut any contact of the Iranians with the outside world," he said. "They are afraid of the BBC in particular because its journalists worked in Iran until recently and have a better understanding of the Iranian society."

Bahari, who has written a book about his experience in jail named Then They Came For Me, said: "I know the imprisoned film-makers and I believe Iran has absolutely no evidence against them but is now resorting to fabricating charges in order to implicate them or make them to confess."

Bahari – whose forced confession was broadcast by Iran's state-run Press TV while in jail – said the broadcast of the Khamenei documentary by the BBC triggered the arrests.

Kamnoosh Shahabi, the sister of the imprisoned distributor, said Katayoun Shahabi had been denied access to her lawyer since her arrest: "The authorities asked us not to speak to media but we are extremely worried and we have no other choice."

She said the irony is that her sister has been praised by the Islamic republic in the past for her contribution to Iran's film industry.